This invention refers to an automatic locking device for pressure-cooker lids, designed to prevent the opening of the latter when there is some internal pressure.
Known pressure-cookers (for the cooking of food) are of the type comprising a cylindrical container or pot and a lid, designed to close the container from inside against a circular seat along the edge of the top opening of the aforementioned container; a lever or handle is pivoted to the lid and is provided with a cam-shaped portion which acts against a supporting crossbar, the ends of which rest on the edge of the container opening so as to clamp the peripheral edge of the lid against the circular seat of the above opening. The advantage of such kinds of pressure-cookers is that the pressure inside the cooker pushes the lid against the circular seat of the container opening during the cooking, and thus contributes to a better seal of the cooker.
Although the lids of said cookers are usually provided with suitable safety valves or devices, so as to prevent the internal pressure from exceeding certain dangerous peaks, the removal of the lid in order to open the pressure-cooker is generally hampered by the internal pressure itself, which causes the lid to adhere firmly to the aforementioned circular seat.
This feature is of great help since it makes sure that an absent-minded person cannot open the pressure-cooker accidentally by operating the closing lever, and cause damage to himself and to any person near him.
In order to open the pressure-cooker, it is therefore necessary to first let the inside steam out by opening an appropriate relief valve, or else let the pressure-cooker and its content cool so as to allow the internal pressure to drop and thus reach the atmospheric pressure level. Manufacturers usually supply detailed instructions in order to guarantee absolute safety when opening a pressure-cooker. On the other hand, when the internal pressure has dropped to minimal values (in the region of 0.1-0.2 Atm.), due to partial steam discharge or to partial content cooling, it is possible to ignore the aforementioned instructions, which prescribe that the closing lever can be operated only after the complete discharge of the steam from the relief valve, hence opening the lid before time when there still is some internal pressure residue.
At such values, in fact, the steam pressure alone is no longer capable of ensuring adequate pressure of the lid against the sealing seat; it is therefore possible to open the pressure-cooker by operating the closing lever. Under such conditions, the removal of the lid may sometimes lead to the emission of a certain quantity of high-temperature liquid and/or steam. An object of this invention, therefore, is to provide a device capable of eliminating any possibility of using the abovementioned kind of pressure-cookers in an improper way, by endowing the lid with a suitable safety device which allows operation of the lid-closing lever only when the pressure inside the same has dropped to values substantially equal to the atmospheric pressure value.
A further object of this invention is to provide a lid-locking device capable of preventing the cooker from opening accidentally while still under the action of internal pressure, which be structurally simple, strong, easy to fit onto the lid and which may, in any case, allow to act on the device itself, after having taken all necessary precautions, in the event of jamming or failure of the device in such a position as to prevent the removal of the lid.